Lakes are organic pigments made by absorbing a dye onto a substrate such as Alumina hydrate or Barium sulphate. They are dispersible (but not soluble) in both water and oil. Lakes will give a matte colour but are much more vibrant than oxides.
The term D&C means that a lake is approved by the FDA for use in drugs and cosmetics.
The number, e.g. Blue #1, refers to which dye has been used to make the lake.
Lakes will have a mineral in their name, e.g. Barium, this is the substrate onto which the dye has been absorbed
Each substrate can absorb a varying amount of each dye. The dye percentage simply tells us how much pure colour is in the lake.